Alternating-current motor



July 5 1927.

J. 1. HULL ALTERNATING CURRENT MOTOR Filed April 25. 1924 H is Attorn ey20 load. In order to en an tion of excessive voltage by transformer acastion and to use a compensator for controlling am] July 5,1921.

g 4. 1 UNITED STATES PATOENTVIOFFICE.

-J'OHN I. HULL, OI

SCHENECTADY, NEW YORK, ASSIGNOR 'l'O GENERAL ELECTRIC comm, ACORPORATION OF NEW YORK.

nrma'rme-cunimn'r MOTOR.

Application fled April 28, 1824. Serial No. 708,552.

5 of being accelerated from rest to synchronous speed without the use ofexternal devices.

It is well known that the operating characteristics of asynchronousmotor and an lo'induction motor differ both with respect to the torqueavailable at starting and the magnetizin' current taken from the lineduring norma operation. The a synchronous motor when brought up to speedwill op- 18, erate at-a power factor dependent on the value of itsexciting current but has no starting torque except. as developed bysimultaneous induction motor action. The induction motor is ca able ofstartin under rin the sync ronous machine up to speed, it as thereforebeen customar to start it with its field circuit arranged to prevent theproducthe voltage applied to its armature winding.

With this arrangement the machine is started as an induction motor, thedamper wind ings serving as a short-circuited secondary 3o circuit. Thestarting torque thus produced is somewhat augmented by the eddy currentsset up in the pole faces of the machine. When the machine has come up tospeed as an induction motor, direct current 1s supplied to its fieldcircuit and it pulls into synchronism. It has also been proposed tostart the synchronous motor with single phase current of slip frequencysupplied to- 'its field circuit, the field excltation being reversed intime harmony with the passage of the olar re ions of the rotatinarmature fie d over t e faces of the exciting field poles. This methodof startin has the disadvantage that, due to the c anging frequency ofthe exciting current, adjustable external reactors and resistors mustbeused to maintain-the proper phase relation between the exciting fieldand the rotating field of the armature.

chine or from a commutator winding placed on the armature core of themachine.

I propose to provide a motor which may.

With either method of starting the exciting current may be suppliedeither from a separate exciting ma-' be accelerated from rest tosynchronous speed without the use of external devices.

To this end I provide either a squirrel cage windin having sufiicientresistance to produce t e required starting torque or a secondarywinding permanently connected across a. resistor for producing the torue at starting, and so interrelate the impe ance of the 'excitin andstarting windings as to preclude the ow of excessive current in theexciting circuit during the starting period, thus eliminating injurioussparking at the commutator of the exciting winding when the fieldcurrent is of high frequency and.

producing a phase relation between the exciting current and the rotatingfield of the armature required to synchronism when it us come up tospeed as an induction motor.

My invention will be better understood on reference to the followingdescriptionwhen considered in connection with the accom panyin drawingand its scope will be pointed out y theappended claims.

Referring now to the drawing, Fig. 1 is a diagrammatic representation ofa motor all the machine into in which my invention has been embodied;

Fig. 2 shows a motorwhich differs from that shown by Fig. 1 in resp ctto the arrangement and number of phases of the stator winding; Fig. 3shows a different arrangement of thestator winding; Fig. 4 1s asectional view showing the arrangement of the windings in the statorslots; and Fig. 5 shows various curves illustrating the operatingcharacteristics of the motor.

Fig. 1 shows a motor the rotor member of which is provided with acommutator winding 1 and a polyphas'e' winding 2 arranged to besuppliedwith alternating current through leads 3, brushes 4 and slip rings 5. Apair of brushes 6 are operatively associated with'the commutator of thewinding 1 to interconnect it with the polyphase stator winding 7 whichfunctions both as a starting and direct current field winding.

Each phaseof the stator winding-7 is permanently connected'across adifferent one of the resistors 8. Impedance means illustrated as areactor 9 is connected in series. with the brushes 6 for the purpose ofreducing the flow of high frequency current in the circuit of thecommutator winding at start- I ing, which reaction disappearsatsynchroenough as compared with that of the re nous speed and thuspermits exciting current at starting to how and synchronize the machine.

- With this arrangement the machine will start substantially like aninduction motor with its secondary winding connected across theresistors 8, the magnitude of the resistance of which must be acompromise between that required to give maximum starting torque andthat which does not give a slip large enough to prevent the motor fromchanging. from in uction to synchronous motor operation under heavyloads. As the motor comes u to speed the frequency of the current suppied through the brushes 6 decreases until at synchronism the frequencyis zero and direct current is supplied from the winding 1' to thewinding 7. Un-

der these conditions the reactor 9 offers no opposition to the currentsupplied to the winding 7, the resistance of which is low sistors 8, toinsure that a comparatively small amount of energy will be consumed inthe rheostats under normal running conditions.

Fig. 5 shows a plurality of curves 0 to e inclusive illustrating thestarting characteristics of the motor for different values of resistancein the resistors 8 connected across the difierent phases of the win 7.The

horizontal curve f is drawn to in 'cate the synchronous: speed of themachine. If the resistors 8 are given a value of resistance correspondintot-he curve I), for example, the motor Wlll follow this curveapproximately until the point g at which the motor tends to synchronizeis reached when it will change over to synchronous speed andoperateonthecurvefr The motor illustrated by 2 is provided with a'stator circuit comprising the two :eaparate phase windings 10 and 11arrang in quadrature with each other and each permanentlyshort-circuitedby a resis tor 8. It'will be apparent that thesewindstarting the .win

mgs may be replaced by a high resistance squirrel cage winding ifdesired. During 10 and 11 function as a two hase short circuitedsecondary winding. on normal running conditions have been attained thedirect current excitation for the motor is produced through the 7 -10alone and thewindizng 11 does not aid in rod the p notion of torquebecause of the fact that the rotating field produced by the win2isstationaryinspace. Thereac: tor 9- ctions in the same manner as inthe arr ement' shown in Fig. 1.

F1 3s ows an I; ent of the motorfj which difiers i: m that of Fig. '2 pin that independent and permanently shortcircuited St8t01' windings 1eare' -provided for starting p alone, a se arate winding 15 being toproyi e the excitaaid in the production of torque uring synchronousoperation, but since they are permanently short-circuited they obviouslyfunction to prevent hunting in a manner similar to the usual damperwinding of the synchronous machine.

As illustrated in Fig. 4 the windin s 13 are preferably placed in a setof perip eral slots near the air gap while the windm 15 is placed in aset of deeply embedded s ots, mm of radial slots in the difierent setsin interconnected by a narrow slot 16 for 51c urpose of making thereactance of the win ing 15 high as compared with that of the windings13. with this arrangement the reactor in the excitin the machine may beomitted. nder these conditions the motor starts. mainly as an inductionmotor, the windings 13 serving as the secondary circuit and theresistors 8,

15 the current init is limited to a comparatively low value d the 'od.The remstors 8 could the omitted i and a squirrel cage winding ofsuitably hi resistance substituted for 13.

have explained my invention by illustrating and describing certain crembodiments' thereof, but it will readily understood by them skilledinthe art that the invention ma be embodied in man other forms than th I,accor to the closed erein by way of example for the poi 130cc of settingforth my invention in acco ance with the dpatent statutes. The terms ofthe appen ed claims are, therefore, not restricted to the precisestructure d1sclosed,but' are intended to cover all changes andmodifications within the spirit and scope of my invention.

What I claim-as new and desire to secure by Letters Patent of the UnitedStates is:

1. Analternating current motor comprisose shown and descri circuit ofarticular forms of construction dising two relatively movable polyphasewind- @or; an exciting, circuit including a c0mmu= tater inductivelyandimmovabliy .associated'with one of said pol hase win 'ings for supplyingthe excitatlon of said motor; means permanently associated with saidcircuit for limiting its current during accelerationof said motor; andmeans perhases of the other of said polyphase-windmgs for improving thestarting characteristics of said moton- 2.-A- synchronous motorrelatively movable polyphase in-' ductively associated with each otherto pro- .manently connected acrom the difierent I I! duce torque foraccelerating said motor; an exciting circuit including a commutatorwinding immovably associated with one of said polyphase windings and afield winding inductively and immovably associated with the other ofsaid polyphase windings for carrying direct current excitation for saidmotor, said exciting circuitbeing arranged to limit the current in saidcircuit during acceleration of said motor, and resistors permanentlyconnected across the different phases of the other of said polyphasewindings for improving the starting characteristics of said motor.

3. An alternating current motor comprising a winding adapted tobetsupplied with polyphase alternating current; an exciting circuitincluding a commutator winding inductively and immovably associated withsaid polyphase winding and a field winding arranged in a set of deeplyembedded slots and movably related to said polyphase Winding forcarrying direct current excitation for said'motor and a starting windingarranged in a setof peripheral slots, radial pairs of slots in the twosets being interconnected by slits for increasing the magnetic leakagebetween said starting and field windings durin acceleration of saidmotor.

In witness. w ereof, I have hereunto set my hand this 22nd day of April,1924.

' i 4 JOHN I. HULL.

